1) Field of the Invention
This invention relates to novel benzoxazine derivatives and salts thereof, which are useful as medicinal drugs, especially as preventives or therapeutics for circulatory diseases or bronchial diseases.
2) Description of the Related Art
As preventives or therapeutics for circulatory diseases led by ischemic heart diseases such as angina pectoris and myocardial infarction and including hypertension or bronchial diseases such as bronchial asthma, pharmaceuticals having smooth muscle relaxing effects, for example, direct smooth muscle relaxing agents, calcium antagonists, .beta.-blockers, .alpha.-blockers and the like have heretofore been used widely. However these pharmaceuticals are all accompanied by one or more drawbacks such as insufficient pharmacological effects and/or high side effects, leading to the outstanding desire for the development of more effective and safer therapeutics.
In the meantime, smooth muscle relaxing agents--which act in accordance with a new mechanism, that is, to activate the potassium channel in smooth muscle cells--have been developed in recent years. They have attracted interests as therapeutics for the abovementioned circulatory diseases or bronchial diseases. Known examples of compounds having such potassium channel activating effects include cromakalim [(.+-.)-trans-6-cyano-2,2-dimethyl-4-(2-oxopyrrolidin-1-yl)-3,4-dihydro-2H -1-benzopyran-3-ol].
These potassium channel activating agents are however still not considered to be fully satisfactory medicinal drugs when they are evaluated in view of both aspects of effectiveness and safety. It has therefore been desired to develop potassium channel activating agents which are still safer and more effective.